The proposed research will define the causes of variability in reproduction in marmosets and tamarins. Examination of variability in callitrichid reproduction serves two functions. First, it is necessary for the formulation of solutions to the problem of high perinatal loss common in these species. Solution of this problem is particularly important in the case of the cotton-top tamarin (Saguinus oedipus), a species which is endangered and an important research resource in studies of colon cancer and EB-V infection. Previous studies have addressed the role behavior plays infant mortality, but clearly more sophisticated, detailed information on reproductive processes in callitrichids is now needed to fully address the problem. Secondly, callitrichids offer unique possibilities to examine the relation of ovulation rate, embryo loss and neonatal mortality to environmental and physiological factors in a primate with a relatively large and variable litter size. The first goal of the proposed research is to determine whether there are differences in the mechanisms controlling ovulation rats in callitrichids with differing ovulation rare. Specifically, endocrine correlates of ovulation rate, timing of follicular recruitment and selection, and pituitary-ovarian feedback systems will be examined in subjects with differing ovulation rates. The second goal is to examine the relation of nutrition and genetics to litter size and offspring viability by monitoring ovulation rate and embryo loss in females of known genetic background on experimental diets. Specifically, the effects of differences in protein and calorie intake in adult females and calorie intake in your growing females will be determined. The third goal of the proposed research is to better define the factors determining litter size and perinatal loss by determining the relation of ovulation rate and embryo survival to litter size and determining the relation of perinatal events and infant birth condition to infant mortality.